/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/************************************************************************
 * kernel/sched/sched_mergepending.c
 *
 *   Copyright (C) 2007, 2009, 2012 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ************************************************************************/

/************************************************************************
 * Included Files
 ************************************************************************/

#include <tinyara/config.h>

#include <stdbool.h>
#include <sched.h>
#include <queue.h>
#include <assert.h>

#include "sched/sched.h"

/************************************************************************
 * Pre-processor Definitions
 ************************************************************************/

/************************************************************************
 * Private Type Declarations
 ************************************************************************/

/************************************************************************
 * Global Variables
 ************************************************************************/

/************************************************************************
 * Private Variables
 ************************************************************************/

/************************************************************************
 * Private Function Prototypes
 ************************************************************************/

/************************************************************************
 * Public Functions
 ************************************************************************/

/************************************************************************
 * Name: sched_mergepending
 *
 * Description:
 *   This function merges the prioritized g_pendingtasks list into the
 *   prioritized g_readytorun task list.
 *
 * Inputs:
 *   None
 *
 * Return Value:
 *   true if the head of the g_readytorun task list has changed.
 *
 * Assumptions:
 * - The caller has established a critical section before
 *   calling this function (calling sched_lock() first is NOT
 *   a good idea -- use irqsave()).
 * - The caller handles the condition that occurs if the
 *   the head of the sched_mergTSTATE_TASK_PENDINGs is changed.
 *
 ************************************************************************/

bool sched_mergepending(void)
{
	FAR struct tcb_s *pndtcb;
	FAR struct tcb_s *pndnext;
	FAR struct tcb_s *rtrtcb;
	FAR struct tcb_s *rtrprev;
	bool ret = false;

	/* Initialize the inner search loop */

	rtrtcb = (FAR struct tcb_s *)g_readytorun.head;

	/* Process every TCB in the g_pendingtasks list */

	for (pndtcb = (FAR struct tcb_s *)g_pendingtasks.head; pndtcb; pndtcb = pndnext) {
		pndnext = pndtcb->flink;

		/* Search the g_readytorun list to find the location to insert the
		 * new pndtcb. Each is list is maintained in ascending sched_priority
		 * order.
		 */

		for (; (rtrtcb && pndtcb->sched_priority <= rtrtcb->sched_priority); rtrtcb = rtrtcb->flink) ;

		/* Add the pndtcb to the spot found in the list.  Check if the
		 * pndtcb goes at the ends of the g_readytorun list. This would be
		 * error condition since the idle test must always be at the end of
		 * the g_readytorun list!
		 */

		ASSERT(rtrtcb);

		/* The pndtcb goes just before rtrtcb */

		rtrprev = rtrtcb->blink;
		if (!rtrprev) {
			/* Special case: Inserting pndtcb at the head of the list */
			/* Inform the instrumentation layer that we are switching tasks */

			sched_note_switch(rtrtcb, pndtcb);

			/* Then insert at the head of the list */

			pndtcb->flink = rtrtcb;
			pndtcb->blink = NULL;
			rtrtcb->blink = pndtcb;
			g_readytorun.head = (FAR dq_entry_t *)pndtcb;
			rtrtcb->task_state = TSTATE_TASK_READYTORUN;
			pndtcb->task_state = TSTATE_TASK_RUNNING;
			ret = true;
		} else {
			/* Insert in the middle of the list */

			pndtcb->flink = rtrtcb;
			pndtcb->blink = rtrprev;
			rtrprev->flink = pndtcb;
			rtrtcb->blink = pndtcb;
			pndtcb->task_state = TSTATE_TASK_READYTORUN;
		}

		/* Set up for the next time through */

		rtrtcb = pndtcb;
	}

	/* Mark the input list empty */

	g_pendingtasks.head = NULL;
	g_pendingtasks.tail = NULL;

	return ret;
}
